<!DOCTYPE html>
<html>
	<head>
		<meta charset="utf-8" />
		<title></title>
	</head>
	<body>
		<script type="text/javascript">
			var arr1=[1,2,3,4,3,2,1];
			var arr2=[];
			for(var i = 0; i<arr1.length;i++){
				arr2.indexOf(arr1)
			}
		</script>
	</body>
</html>